Human Digestive System: Stages and Processes

Human Digestive System Processes

Digestion involves two main types of processes:

• Mechanical Digestion: Food is ground, cut, and mixed with juices.
• Chemical Digestion: Food is broken down by hydrolytic enzymes.

1. Digestion in the Mouth

Mastication

This is the mechanical process involving the teeth and tongue. Food is torn and ground into small pieces.

Insalivation

Food is mixed with saliva. Pieces of food are moistened to form a bolus. Saliva is produced by the salivary glands and contains:

• Salivary Amylase: Responsible for the digestion of starch.
• Mucin: Gives viscosity to the saliva.
• Lysozyme: Attacks bacteria.

2. Deglutition (Swallowing)

The food bolus moves from the mouth towards the pharynx and passes the epiglottis. The bolus then enters the oesophagus, where it is moved by the contraction and relaxation of two muscle layers. This movement is called peristalsis.

3. Gastric Digestion

The cardiac sphincter produces gastric acid, and the stomach begins to move. Key components include:

• Hydrochloric Acid (HCl): Eliminates microorganisms.
• Pepsin: An enzyme that breaks the bonds between the amino acids in proteins.

4. Intestinal Digestion

Chyme comes from the stomach into the small intestine. Digestion here is aided by:

• Pancreatic Juice: Digests polysaccharides, fats, and proteins.
• Bile: Helps to digest fats by breaking them up (emulsification).
• Intestinal Juice: Digests proteins, sugars, fats, and nucleic acids.

5. Absorption

Nutrients are absorbed by the intestinal villi. Nutrients pass through the epithelial cells into the capillaries. Substances that have not been absorbed move to the large intestine.

6. Egestion

Substances fermented by the intestinal flora are compacted to form faeces. Faeces are excreted via the anus.